As shown in FIG. 23, an existing method to attach a denture on the gingiva by a dental magnetic attachment is as follows. Root cap 102 is set on the tooth root 101 in the gingiva to form an abutment tooth for the denture 110. A keeper 103 made of corrosion-resisting soft magnetic alloy is embedded in the center of top surface of root cap 102. A dental attachment 111 is embedded in the center of bottom face of the denture so as to face the keeper 103. The attachment 111 attracts the keeper 103 magnetically, thus the denture 110 is fixed on the root surface 102.
Japanese patent application Laid-Open (Kokai) No. 1-303145, 2-295557, 2-295558 disclose a dental attachment 111 of which exploded view is shown in FIG. 24, sectional view in FIG. 25. This existing attachment consists of a block of magnet 112, a spacer 113 made of corrosion resisting non-magnetic alloy to cover one face of the magnet, a pair of yokes 114, 115 that made of corrosion resisting soft magnetic alloy to sandwich the magnet 112 and the spacer 113 in between, and a cap 116 made of corrosion resisting non-magnetic alloy to cover whole other parts. This dental attachment has a magnet 112 with the N-S direction parallel to the keeper 113. A magnetic circuit is formed in which the magnetic flux generated at the magnet 112, passes through the yoke 114, keeper 103, then the other yoke 105, finally returns to the magnet 112. This closed magnetic circuit gives relatively strong attractive force.
Japanese patent application Laid-Open (Kokai) No. 57-164054 disclose a dental attachment 121 of which magnet arrangement is shown in FIG. 26. The attachment in the denture is shown in FIG. 27. This dental attachment consists of plurality of pairs of permanent magnet 122 and soft magnetic part 123. The permanent magnets 122 and the soft magnetic parts 123 are arranged alternatively so that the like magnet poles face each other. When a soft magnetic body, so called attachment keeper, is placed in contact with the attachment 121, almost all magnetic flux pass along the keeper so that it is attracted to the attachment 121 quite firmly.